How to display flat data structure into hierarchical data structure (Java)?

Question

I have recently faced this question in a practical test for a job .

Suppose you are given a flat data structure like this :

**Category**         **Name**         


        

Answer 1

public class FileReader {
    Map employees;
    Employee topEmployee;
    class Employee {
        int id;
        int mgrId;
        String empName;
        List subordinates;
        public Employee(String id, String mgrid, String empName) {
            try {
                int empId = Integer.parseInt(id);
                int mgrId = 0;
                if (!"Null".equals(mgrid)) {
                    mgrId = Integer.parseInt(mgrid);
                }
                this.id = empId;
                this.mgrId = mgrId;
                this.empName = empName;
            } catch (Exception e) {
                System.out.println("Unable to create Employee as the data is " + id + " " + mgrid + " " + empName);
            }
        }

        List getSubordinates() {
            return subordinates;
        }
        void setSubordinates(List subordinates) {
            this.subordinates = subordinates;
        }
        int getId() {
            return id;
        }

        void setId(int id) {
            this.id = id;
        }

        int getMgrId() {
            return mgrId;
        }

    }

    public static void main(String[] args) throws IOException {
        FileReader thisClass = new FileReader();
        thisClass.process();
    }

    private void process() throws IOException {
        employees = new HashMap();
        readDataAndCreateEmployees();
        buildHierarchy(topEmployee);
        printSubOrdinates(topEmployee, tabLevel);
    }

    private void readDataAndCreateEmployees() throws IOException {
        BufferedReader reader = new BufferedReader(new java.io.FileReader("src/main/java/com/springapp/mvc/input.txt"));
        String line = reader.readLine();
        while (line != null) {
            Employee employee = createEmployee(line);
            employees.put(employee.getId(), employee);
            if (employee.getMgrId() == 0) {
                topEmployee = employee;
            }
            line = reader.readLine();
        }
    }

    int tabLevel = 0;

    private void printSubOrdinates(Employee topEmployee, int tabLevel) {
        for (int i = 0; i < tabLevel; i++) {
            System.out.print("\t");
        }
        System.out.println("-" + topEmployee.empName);
        List subordinates = topEmployee.getSubordinates();
        System.out.print(" ");
        for (Employee e : subordinates) {
            printSubOrdinates(e, tabLevel+1);
        }
    }
    public List findAllEmployeesByMgrId(int mgrid) {
        List sameMgrEmployees = new ArrayList();
        for (Employee e : employees.values()) {
            if (e.getMgrId() == mgrid) {
                sameMgrEmployees.add(e);
            }
        }
        return sameMgrEmployees;
    }

    private void buildHierarchy(Employee topEmployee) {
        Employee employee = topEmployee;
        List employees1 = findAllEmployeesByMgrId(employee.getId());
        employee.setSubordinates(employees1);
        if (employees1.size() == 0) {
            return;
        }

        for (Employee e : employees1) {
            buildHierarchy(e);
        }
    }

    private Employee createEmployee(String line) {
        String[] values = line.split(" ");
        Employee employee = null;
        try {
            if (values.length > 1) {
                employee = new Employee(values[0], values[2], values[1]);
            }
        } catch (Exception e) {
            System.out.println("Unable to create Employee as the data is " + values);
        }
        return employee;
    }
}